1. Field of the Invention
The present invention relates to a novel transglutaminase and a process for producing a protein gelation product using the transglutaminase.
2. Description of the Background
Transglutaminases are enzymes which catalyse an acyl transfer reaction of a .gamma.-carboxyamide group of a glutamine residue in a peptide chain.
The transglutaminases form intramolecular or intermolecular .epsilon.-(.gamma.-Glu)-Lys cross-linking wherein the .epsilon.-amino group of the lysine residue in the protein serves as the acyl receptor. When water functions as the acyl receptor, the transglutaminases catalyze deamination of glutamine residues to form glutamic acid residues.
The gelation products of the present invention produced utilizing the novel transglutaminases are used as yoghurt, jelly, cheese, gel cosmetics, etc., including conventional gel foodstuffs and gel cosmetics. Furthermore, the gelation products in accordance with the present invention can be produced in a non-heated state and are thermally stable and therefore, can also be used over a wide range, such as raw materials for microcapsules, carriers for immobilized enzymes, etc.
Transglutaminases hitherto known are those derived from animals. Transglutaminases are widely distributed in, for example, liver of the guinea pig [Connellan, et al., Journal of Biological Chemistry, vol. 246, No. 4, pages 1093-1098 (1971)] and mammal organs and blood [Folk et al., Advances in Enzymology, vol. 38, pages 109-191 (1973) and Folk et al., Advances in Protein Chemistry, vol. 31, pages 1-133 (1977)] and, characteristics of the enzymes have been investigated.
Up to now, however, no report has been made on any transglutaminase derived from microorganisms. With respect to a process for producing gel products of protein using an animal-derived transglutaminase, the present inventors have already made investigations resulting in Published Unexamined Japanese Patent Application No. 149645/83.
However, application of the animal-derived transglutaminase to industry, particularly, the process for producing protein gelation products involves defects as described below.
It is difficult to obtain animal-derived transglutaminases at low cost and in large quantities. Also, there is the restriction that at least 1 unit of this expensive enzyme per 1 g of substrate protein and at least 2.0 wt. % of a substrate protein concentration are required for gelation. Further, the animal-derived transglutaminase is calcium (Ca.sup.2+)dependent so that its application is limited.
Because of the foregoing defects, processes for producing gelation products using animal-derived transglutaminases are impractical.